POS0037 VALIDATION OF DIAGNOSTIC CODES FOR DEMENTIA IN A RHEUMATOID ARTHRITIS POPULATION-BASED COHORT
Authors: E. Myasoedova, M. Vassilaki, C. Kodishala, E. Lovering, R. Kumar, C. S. Crowson
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Dementia is a major global mental health problem. The prevalence of dementia is increasing dramatically with increasing life longevity and population aging. Several studies found increased risk of dementia in patients with rheumatoid arthritis (RA) and reported a possibility of mitigating this risk with antirheumatic treatments. The underlying mechanisms for these associations are not fully understood and require further study. As clinical verification of the diagnosis may not be readily available, especially in retrospective observational studies, diagnostic codes can be used. However, performance of diagnostic codes for dementia case identification has not been validated in RA cohorts. <h3>Objectives</h3> To validate the use of ICD-9/10-CM diagnostic codes for dementia identification against diagnostic criteria for dementia in individuals with and without RA using retrospective manual verification of cases. <h3>Methods</h3> This retrospective population-based study included residents of a geographically well-defined area with incident RA based on the 1987 American College of Rheumatology (ACR) classification criteria in 1980-2018. All adult (≥18 years) cases of RA were included and matched (1:1) by age, sex, calendar year, and county to non-RA controls. Dementia case identification using ICD-9/10-CM diagnostic codes from the Charlson comorbidity index was validated against dementia diagnosis based on Diagnostic criteria in Diagnostic and Statistical Manual of Mental Disorders, 4<sup>th</sup> edition (DSM-IV). DSM-IV criteria were verified by manual records review. <h3>Results</h3> A total of 3,116 individuals (1558 RA cases and 1558 non-RA controls) were included. Mean age 56.2 years; 68% females in both groups; mean (SD) age at the last follow-up was 68.7 (14.7) years for RA cases and 69.6 (15.4) years for non-RA controls. At the time of the last follow-up, there were 202 (13%) patients with one diagnostic code for dementia, 136 (9%) with two diagnostic codes for dementia, and 137 (9%) with a confirmed diagnosis of dementia per DSM-IV. The respective numbers in non-RA controls are 216 (14%); 147 (9%) and 149 (10%). Mean (SD) duration between accumulating two ICD codes and diagnosis verification by DSM-IV was an absolute difference of 1.0 (1.8) years in RA and 1.2 (1.7) years in non-RA. Table 1 summarizes the results of validation analyses. Positive predictive value (PPV) and specificity were higher with the use of 2 ICD codes in the combined cohort (PPV 81.3), in RA cases (PPV 81.6) and in non-RA controls (PPV 80.9). PPV for two diagnostic codes was highest also in patients born in 1892-1934 (PPV 85.7) than in the more recent birth cohorts: 1935-1949 (PPV 77.6). <h3>Conclusion</h3> The ICD-9/10-CM codes for dementia performed equally well against DSM-IV criteria in the retrospective population-based cohort of individuals with RA and in matched non-RA controls, identifying true dementia cases with approximately 80% probability. The PPV was higher in older birth cohorts than in younger birth cohorts, reflecting the higher prevalence of dementia in older adults. The use of ICD-9/10-CM codes from Charlson comorbidity index is acceptable for dementia case identification in patients with RA, especially in older adults, although additional parameters (e.g., number of diagnostic codes) need to be considered. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Elena Myasoedova: None declared, Maria Vassilaki Shareholder of: equity ownership in Abbott Laboratories, Johnson and Johnson, Medtronic, AbbVie, Merck and Amgen, Consultant of: F. Hoffmann-La Roche Ltd, Grant/research support from: F. Hoffmann-La Roche Ltd and Biogen, Chanakya Kodishala: None declared, Edward Lovering: None declared, Rakesh Kumar: None declared, Cynthia S. Crowson: None declared.